North Korea has been building up what look like missile test pads on five islands in the Yellow Sea.

What used to be deserted wasteland has been transformed into strategic outposts constructed close to the city of Sohae, a major missile development and testing site around 200 kilometres northwest of Pyongyang.

Some of the built-up are entirely man-made “artificial islands” in the style of those built by the Chinese in the South China Sea to claim the land over Malaysia, the Philippines, Taiwan, Brunei and Vietnam.

The islands feature what appear to be missile launch pads or underground silos and observation areas, which could be used by Kim Jong-un, who likes to keep a close eye on the construction and operation of military facilities.

North Korea has been building up what look like missile test pads on five islands in the Yellow Sea. Picture: Google MapsSource:Supplied

Wide roads suitable for missile launch trucks, rectangular patches that could be launch pads are visible on the islands. Picture: Google MapsSource:Supplied

The islands all appear to be different sizes and shapes, with wide roads suitable for missile-bearing trucks leading to pale rectangular areas. This could indicate heat-resistant cement, ideal for launching the intercontinental ballistic missile technology that is developed at Sohae.

In Google Earth images from 2012, several of the islands look like no more than patches of sand, rock and scrubland.

The Diplomat has dubbed them “the Sohae Islands” because of their proximity to the military structure.

North Korea’s missile launch stations are typically located in the mountains, so the positioning of these islands in the sea that is also bordered by China is unusual. The location could be appropriate for anti-aircraft or anti-ship area denial weapons, however.

If the aim is to deploy surface-to-air missiles, more infrastructure will be needed including radar and command posts.

It is also possible the facilities are for oil exploration, since the Yellow Sea is “full of oil”, North Korea expert Dr Leonid Petrov told news.com.au. The sea has estimated reserves of billions of tonnes but a lack of collaboration between the two countries has held back the exploitation of it.

In the recent past, there were also clashes between the two countries on the Yellow Sea, when North Korea would arrest Chinese fishermen and others until their companies paid a ransom. “It could be strategic or for oil exploration,” said Dr Petrov.

Some of the outposts are entirely artificial, just like those developed by the Chinese in the South China Sea. Picture: Google MapsSource:Supplied

What look like observation decks can also be seen. Kim Jong-un is known to like to oversee military construction and operations. Picture: Google MapsSource:Supplied

“Every time we see VIP buildings, that tells us there’s most likely a military application, because Kim Jong-un likes to view the operations of whatever they’re building,” Ryan Barenklau, chief executive of intelligence firm Strategic Sentinel told the LA Times.

“At first we were really concerned about what the initial purpose of those islands are — whether they’re for military or agriculture purposes — but when we saw the observation decks, we thought, those are military.”

Some of the islands are part of the Taegyedo Tideland Reclamation Project, which began decades ago and finished in 2012, converting the area to hold a fish farm, duck farm and oyster farm.

It is possible the developments have agricultural or other civilian purposes, but North Korea has in the past used civilian construction projects for an additional military purpose.

Steve Sin, a researcher on unconventional weapons and technology at the University of Maryland, told the Times “the North Koreans build just about everything for dual purpose.”

The islands could be for agricultural or civilian projects, but the state has been known to convert civilian structures for military purposes. Picture: Google MapsSource:Supplied

The islands are positioned close to Sohae, a major ballistic missile testing facility.Source:Supplied

He said that if the islands did have military purpose it was probably not to launch long-range ballistic missiles, but could be for shorter-range, more portable missiles such as KN-02 and Scuds. “North Korea still has to stack and fuel those at the launch site itself,” he said.

While the islands are nowhere near as numerous or as developed as the islands China has built up despite competing claims by nearby countries, the move is likely to provoke increased tension in these volatile times.

North Korea’s failed ballistic missile launch last week marked the hermit state’s latest show of defiance after it paraded its weapons and warned it is capable of a nuclear strike. Donald Trump responded by diverting a naval strike group toward the Korean peninsula but this week said he would be “honoured” to meet Kim Jong-un under the right conditions.

China has called for all of its citizens to return from North Korea immediately after a US citizen was detained for allegedly trying to overthrow the country’s regime.

US-based analysts said on Tuesday satellite images indicated activity has resumed at North Korea’s nuclear test site as tensions remain high over fears of an sixth atomic test by the reclusive state.

Images of the Punggye-ri site captured on April 25 appear to show workers pumping out water at a tunnel believed to have been prepared for an upcoming nuclear test, monitoring group 38 North said.

It also noted that a large number of personnel were seen throughout the facility, with some groups possibly playing volleyball, in what is very likely a propaganda scene.

Given the state’s notorious secrecy, the purpose of the islands may remain shrouded in doubt for some time. They could even be a decoy from Kim’s real plans.

One thing is for sure, their shadowy presence will create real anxiety.